Lonliness is a major risk factor for morbidity and mortality from widely varying causes, even after statistically controlling for known biological risk factors (such as smoking, blood pressure, obesity and physical activity), social status and baseline measures of health. The mechanisms underlying the relationship between social factors and health are not yet understood but several different mechanisms are likely involved. To explore these mechanisms, this study will investigate the effects of lonliness and social embeddedness on psychosocial, behavioral, physiological and health-outcome variables.